Such a scroll compressor includes, in a sealed casing, a scroll compression mechanism composed of: a fixed scroll fixed on the casing; and a movable scroll which is driven into travel around the axis of the fixed scroll through a crank shaft by a drive means such as a motor. The fixed scroll is formed such that a volute projects from an end plate. The movable scroll has an end plate opposed to the end plate of the fixed scroll. From the end plate of the movable scroll, a volute projects so as to divide a compression chamber into sections by the engagement with the volute of the fixed scroll. Through the travel of the movable scroll, a gas sucked from the outer peripheries of the volutes of both the scrolls is compressed in the compression chamber.
In the above scroll compressor, from a performance viewpoint, the compression chamber must be kept gastight. Therefore, it is required to eliminate gaps between the end surface of the volute of each scroll and the end plate of the opposite scroll. To satisfy the requirement, there is proposed a conventional technique as disclosed in Japanese Patent Application Laid-Open Gazette No. 3-237287, in which an oil is pumped from an oil reservoir located at a lower part inside of the casing by a supply pump driven by a crank shaft, the oil is supplied to a space between the volutes of both the scrolls through a supply passage inside of the crank shaft and the supplied oil fills gaps created between the end surface of each volute and the opposite end plate. In the above proposed technique, a partition wall divides the inner space of the casing into two chambers, i.e., a discharge chamber filled with a gas discharged from the scroll compression mechanism and a suction chamber filled with a gas sucked into the compression mechanism. The motor and the oil reservoir are placed in the suction chamber.
In the proposed technique, however, the oil having a low pressure is supplied, together with the sucked gas, from the outer peripheries of the volutes of both the scrolls to the compression chamber, which causes the oil to apply heat to the sucked gas. Further, the gas in the suction chamber is heated also by a heat loss of the motor, which decreases a compressor performance.
Furthermore, the proposed technique requires an oil separation mechanism such as a demister for separating the oil mixed with the gas during compression in the compression chamber from the discharged gas and an oil backing mechanism such as a capillary for returning the separated oil to the oil reservoir located on a lower-pressure side in the casing. This invites a rise in cost.
There is also known a conventional technique in which an oil pumped from an oil reservoir by a supply pump is supplied to a bearing for a crank shaft through a supply passage inside of the crack shaft so that the bearing is lubricated by the supplied oil. Also in this case that the oil is supplied to the bearing for the crank shaft, the low-pressure oil is mixed with a sucked gas in a lower-pressure chamber. Accordingly, the present case has the same problem as in the first-described case.
An object of the present invention is to prevent a sucked gas from being heated by a heat loss of a motor or an oil when the oil is supplied for increasing the gas-tightness of a compression chamber or for lubricating a bearing for a crank shaft, thereby increasing a compressor performance and to eliminate a special member for separating the oil from a compressed gas thereby preventing a rise in cost.